Abstract
Volcanic eruptions can trigger tsunamis, which may cause significant damage to coastal communities and infrastructure. Tsunami generation during volcanic eruptions is complex and often due ...to a combination of processes. The 1650 eruption of the Kolumbo submarine volcano triggered a tsunami causing major destruction on surrounding islands in the Aegean Sea. However, the source mechanisms behind the tsunami have been disputed due to difficulties in sampling and imaging submarine volcanoes. Here we show, based on three-dimensional seismic data, that ~1.2 km³ of Kolumbo’s northwestern flank moved 500–1000 m downslope along a basal detachment surface. This movement is consistent with depressurization of the magma feeding system, causing a catastrophic explosion. Numerical tsunami simulations indicate that only the combination of flank movement followed by an explosive eruption can explain historical eyewitness accounts. This cascading sequence of natural hazards suggests that assessing submarine flank movements is critical for early warning of volcanogenic tsunamis.
Despite their global societal importance, the volumes of large-scale volcanic eruptions remain poorly constrained. Here, we integrate seismic reflection and P-wave tomography datasets with computed ...tomography-derived sedimentological analyses to estimate the volume of the iconic Minoan eruption. Our results reveal a total dense-rock equivalent eruption volume of 34.5 ± 6.8 km³, which encompasses 21.4 ± 3.6 km³ of tephra fall deposits, 6.9 ± 2 km³ of ignimbrites, and 6.1 ± 1.2 km³ of intra-caldera deposits. 2.8 ± 1.5 km³ of the total material consists of lithics. These volume estimates are in agreement with an independent caldera collapse reconstruction (33.1 ± 1.2 km³). Our results show that the Plinian phase contributed most to the distal tephra fall, and that the pyroclastic flow volume is significantly smaller than previously assumed. This benchmark reconstruction demonstrates that complementary geophysical and sedimentological datasets are required for reliable eruption volume estimates, which are necessary for regional and global volcanic hazard assessments.
Plutonic rocks such as gabbros provide information on magmatic and tectonic processes which occur beneath a mid-ocean rift axis as well as on the formation of the oceanic crust. Igneous rocks, ...reported from the Red Sea Rift valley, have been limited to extrusive basalts so far. The only deeper crustal rocks found in the Red Sea area are from the rift flanks and are interpreted as late-stage continental rift magmatism. Here, we present the geochemistry of the first recovered gabbro fragments from the axis of the Red Sea Rift, sampled from a crater structure within the brine-filled Discovery Deep at the axis of the Red Sea Rift. Petrology and geochemistry show characteristics of a typical mid-ocean ridge gabbro formed at shallow crystallization depth. Clinopyroxene core mineral data fall within two groups, thus pointing to a multiphased magmatic history, including different magma batches and a joint late-stage fractional crystallization. Geobarometry, based on clinopyroxene cores, suggests lower crystallization pressures than similar geobarometric data reported for gabbroic samples from Zabargad (8–9 kbar) and Brother’s Islands (2.5–3.5 kbar) at the rift flanks. However, based on the evolved whole rock composition, its multiphase history, the thickness of the crust, the current location of the samples, and the uncertainties in the barometer, geobarometric estimates for the samples are likely overestimated. Instead, we propose that these rock fragments originate from the upper part of a fully developed oceanic crust in the central Red Sea Rift. High-resolution bathymetry and sparker seismic data reveal that the Discovery Deep is characterized by a significant normal fault and a strong reflector near the rift axis, which we interpret as a potential sill intrusion in an approximate depth of 400 m. Based on the lack of progressive alteration and the sampling location within a sediment-free crater structure, we interpret that the emplacement of the gabbros has to be geologically recent. We interpret the gabbro either as a xenolith transported by the eruptive volcanism that formed the crater, potentially related to the sill intrusion visible at depth, or as intrusive gabbro, which was uplifted and deposited in a talus fan by the adjacent normal fault, exposed by the formation of the volcanic crater.
The Baltic Basin is known for its numerous Paleozoic hydrocarbon reservoirs. There is published evidence that hydrocarbons are leaking from the seafloor, however, little is known about the ...hydrocarbon migration pathways from Paleozoic source and reservoir rocks toward the seafloor and their escape structures. To investigate these processes, we utilize a new set of multibeam, parametric sediment sub‐bottom profiler and 2D seismic reflection data. The integrated analysis of seismic profiles, diffraction imaging and bathymetric maps allow to identify a hydrocarbon migration system within Silurian and Devonian strata that consists of layer parallel and updip migration beneath sealing layers, migration across seals along faults, and seafloor escape structures in form of elongated depressions. The general migration trend is directed updip, from the Paleozoic reservoirs below the southeastern Baltic Sea toward the Gotland Depression in the northwest. The locations of the hydrocarbon escape structures at the seafloor and their elongated shape are mainly controlled by the regional geological setting of outcropping Paleozoic layers. In addition, iceberg scouring may have facilitated hydrocarbon migration through the Quaternary deposits. The description of this hydrocarbon migration system fills the gap between the known reservoirs and the observed hydrocarbon accumulations and seepages. With regard to potential Carbon Capture and Storage projects, the identification of this hydrocarbon migration system is of great importance, as potential storage sites may be leaking.
Plain Language Summary
The Baltic Basin including the Baltic Sea is well known for its hydrocarbon reservoirs with ongoing oil production since the 1940s. While there is some published evidence that hydrocarbons are leaking from the seafloor, little is known about the pathways from the reservoirs toward theses leakages. In this study, we use three imaging techniques for the seafloor, the uppermost sediments and the first few kilometers of the subsurface to image the hydrocarbon migration pathways and their escape structures. We find that hydrocarbons are migrating along dipped geological layers from the reservoirs in the southeast toward the Gotland Deep in the northwest. Additionally, we also observe that hydrocarbons are penetrating through these geological layers at locations of pre‐existing small‐scale fractures. The locations, at which the hydrocarbons escape from the seafloor, are mainly controlled by the regional tectonic setting. In addition, iceberg scouring may have had an influence on the exact escape locations. With our findings in this study, we fill the gap between the known reservoirs and the observed seepages and can contribute to questions regarding the potential storage of CO2 in the Baltic Basin.
Key Points
Numerous elongated fluid escape depressions are observed at the eastern margin of the Gotland Deep, central Baltic Sea
First evidence for fluid migration pathways from Paleozoic toward Quaternary strata in the region
Locations of fluid escape is controlled by the regional tectonic setting
Abstract
Large explosive volcanic eruptions from island arcs pour pyroclastic currents into marine basins, impacting ecosystems and generating tsunamis that threaten coastal communities and ...infrastructures. Risk assessments require robust records of such highly hazardous events, which is challenging as most of the products lie buried under the sea. Here we report the discovery by IODP Expedition 398 of a giant rhyolitic pumice deposit emplaced 520 ± 10 ky ago at water depths of 200 to 1000 m during a high-intensity, shallow submarine eruption of ancestral Santorini Volcano. Pyroclastic currents discharged into the sea transformed into turbidity currents and slurries, forming a >89 ± 8 km
3
volcaniclastic megaturbidite up to 150 m thick in the surrounding marine basins, while breaching of the sea surface by the eruption column laid down veneers of ignimbrite on three islands. The eruption is one of the largest recorded on the South Aegean Volcanic Arc, and highlights the hazards from submarine explosive eruptions.
Abstract
The Christiana‐Santorini‐Kolumbo (CSK) volcanic field has hosted more than 100 explosive eruptions in the past 250,000 years, including the 1650 CE eruption of Kolumbo Volcano. Previous ...studies have established a link between regional tectonics and volcanism in the CSK volcanic field. While 2D seismic reflection data have given valuable insight into regional faulting, detailed fault zone characterization has been precluded by the sparsely spaced profiles. Using 3D seismic reflection data around Kolumbo Volcano, we provide the first 3D characterization of fault zones in the CSK volcanic field. Beneath the volcano's northwestern flank, and farther to the northwest, normal faults are predominantly NE‐SW trending, with mean fault trends between 044° and 049°. Normal faults beneath the southeastern flank are slightly more north‐oriented, with mean fault trends between 028° and 038°. Our detailed fault zone analysis reveals clear NW‐SE directed extension around the volcano, consistent with published focal mechanisms from microseismicity. The Kolumbo Fault Zone, ∼6 km northwest of Kolumbo Volcano, is characterized by distinct relay ramps between major overstepping normal faults. Regional 2D seismic profiles reveal a previously undocumented volcanic cone directly above the fault zone. Magma ascent to this cone has likely exploited enhanced vertical permeability associated with distributed deformation within a relay ramp. We suggest that fault relay structures may play an important role, over a range of spatial scales, in focusing magma ascent within the CSK volcanic field.
Plain Language Summary
In the last 250,000 years, more than 100 explosive eruptions have occurred in the “Christiana‐Santorini‐Kolumbo” volcanic field in the Aegean Sea. Eruptions like these represent a serious natural hazard for the region. In this study, we explored how tectonic processes are related to volcanic activity. We did this by studying tectonic deformation around the submarine Kolumbo Volcano, which last erupted violently in 1650 CE. We used three‐dimensional (3D) seismic reflection data, which provide high‐resolution imagery of the seafloor and underlying sediments. The data set shows how the sediments beneath the seafloor have been disrupted by tectonic faults, which have formed as the crust is being slowly pulled apart (extended). The orientations of the faults show that extension in and around the volcano is happening along a northwest to southeast orientation. Based on our new data, we suggest that the movement of magma through the crust might occur preferentially through structural features called “relay ramps.” Relay ramps are regions of complex tectonic deformation that exist between overlapping extensional faults. Our 3D imagery of fault zones in this volcanic field gives a better understanding of how tectonic and volcanic processes interact with each other.
Key Points
3D seismic data reveal unprecedented detail of normal faulting around the submarine Kolumbo Volcano, Aegean Sea
Long‐term extension (NW‐SE oriented) around Kolumbo Volcano is consistent with previous studies of seismicity and field mapping on Santorini
Relay ramps accommodate strain in step‐overs between normal faults and may be exploited as permeable zones for vertical magma ascent
The Minoan eruption of Santorini is one of the largest Holocene volcanic events and produced several cubic kilometers of pyroclastic flows emplaced on the submerged flanks of the volcano. Marine ...geophysical surveys reveal a multitude of undulating seafloor bedforms (USBs) around Santorini. While similar structures are known from other volcanoes worldwide, Santorini offers the unique opportunity to relate USB formation with volcanic processes during one of the best-studied volcanic eruptions worldwide. In this study, we combine high-resolution seismic reflection data with multibeam echosounder bathymetry to reveal the internal architecture of USBs around Santorini and to relate their morphological characteristics to formational processes. The USBs around Santorini were formed during the Minoan eruption and represent the seafloor expression of mass transport deposits. Three types of deposits differ in composition or origin. (1) Depositional USBs, which can only be found to the north of the island, where Minoan eruption ignimbrites reach their maximum thickness and the undulating topography is the result of thrusting within the deposit. (2) USBs related to slope failures of volcaniclastics from the entire Thera Pyroclastic Formation, which can be found east, south, and west of the island. (3) USBs associated with deep-seated deformation, which occurs on the southwestern flank along an area affected by rift tectonics and extends to a depth of more than 200 m below the seafloor. In cases (2) and (3), the USBs are formed upslope by block rotation and downslope by thrusting. Our study indicates that these processes may have contributed to the generation of the devastating Minoan tsunami. Since Santorini is located in one of the most tectonically active regions in the Mediterranean, capable of producing earthquakes with magnitude M7+, our study has important implications for hazard assessment. A strong earthquake located close to the island may have the potential to reactivate slope instabilities posing a previously undetected but potentially significant tsunami hazard.
•The Minoan eruption formed undulating seafloor bedforms (USBs) around Santorini.•USBs are the result of pyroclastic flows, slope failure and deep-seated deformation.•Deep-seated deformation affects the southwestern flank of Santorini.
The reactivation of faults and possible impact on barrier integrity marks a critical aspect for investigations on subsurface usage capabilities. Glacial isostatic adjustments, originating from ...repeated Quaternary glaciations of northern Europe, cause tectonic stresses on pre‐existing fault systems and structural elements of the North German and Norwegian–Danish basins. Notably, our current understanding of the dynamics and scales of glacially induced fault reactivation is rather limited. A high‐resolution 2D seismic data set recently acquired offshore northeastern Langeland Island allows the investigation of a fault and graben system termed the Langeland Fault System. Seismo‐stratigraphic interpretation of reflection seismic data in combination with diffraction imaging unravels the spatial character of the Langeland Fault System along an elevated basement block of the Ringkøbing–Fyn High. In combination with sediment echosounder data, the data set helps to visualize the continuation of deep‐rooted faults up to the sea floor. Initial Mesozoic faulting occurred during the Triassic. Late Cretaceous inversion reactivated a basement fault flanking the southern border of the elevated basement block of the Ringkøbing–Fyn High while inversion is absent in the Langeland Fault System. Here, normal faulting occurred in the Maastrichtian–Danian. We show that a glacial or postglacial fault reactivation occurred within the Langeland Fault System, as evident by the propagation of the faults from the deeper subsurface up to the sea floor, dissecting glacial and postglacial successions. Our findings suggest that the Langeland Fault System was reactivated over a length scale of a minimum of 8.5 km. We discuss the causes for this Quaternary fault reactivations in the context of glacially induced faulting and the present‐day stress field. The combination of imaging techniques with different penetration depths and vertical resolution used in this study is rarely realized in the hinterland. It can therefore be speculated that many more inherited, deep‐rooted faults were reactivated in Pleistocene glaciated regions.
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